The physiological and biochemial roles of carnitine and taurine in the heart will be studied in several pathophysiological states. Carnitine is an obligate substrate in long-chain fatty acid oxidation, whereas taurine is thought to be involved in a number of membrane processes including ion transport. Because neither carnitine or taurine are synthesized or metabolized in the heart studies on regulation of these compounds will be focused on uptake systems using the isolated beating adult rat myocyte (IBM), and the isolated perfused rat heart, preparation (IPRH) where ventricular pressure development can be assessed. In the IPRH mechanical activity will be followed by sonometric techniques. Models to be studied include the alloxan diabetic rat, and rats treated with diphtheria toxin, adriamycin (doxorubicin), isoproterenol. Assessments of substrate use and choice, ion transport (Na ion, K ion, Ca ions) and mechanical activity will be correlated with changes in cardiac carnitine and taurine. The effects of pharmacologic agents which we know will alter these carnitine and/or taurine levels will be studied. These include: carnitine (4-pentenoic acid, cyclopropane acetate, malonyl-carnitine, 7,8 dihydroxychlorpromazine) and taurine (germitrine, digoxin, guanidinotaurine, verpamil).